The present invention relates to a press die assembly and a method for producing the press die assembly particularly to a shape.
In general, a sheet metal constituting a structure such as an automobile body has surfaces of three-dimensional curvature or double curvature. In many cases, such a structure is fabricated by press forming.
In the press forming of such panel structures, the press die is an important part. The press die usually comprises a punch and a die. A panel as a workpiece is laid on the press die and formed by the punch.
As will be described in detail hereinafter, a recessed surface portion of the press die often has a concave corner portion extending linearly or with a curvature. On the other hand, the punch has a convex corner portion matched to the concave corner portion of the press die. Conversely, the recessed surface portion of the press die has a convex corner portion while the punch has a concave corner portion.
In either case, the concave and convex corner portions tend to interfere with each other unless they are precisely machined so as to avoid any interfering engagement therebetween when the punch plunges into the recessed surface portion of the die. However, precise machining of the concave and convex corner portions requires machining tools of different sizes for different machining processes from a rough machining to a finished machining. Precise machining further requires a numerically controlled three-dimensional machining under various machining conditions such as different cutting speeds for different tools. This is inefficient and time consuming.